The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
An internal combustion engine (ICE) may be operated in a spark ignition (SI) mode and a homogeneous charge compression ignition (HCCI) mode for fuel efficiency and increased engine power. In the SI mode, an air/fuel mixture may be ignited by spark plugs in cylinders of the ICE. In the HCCI mode, an air/fuel mixture may be ignited through compression without ignition by spark plugs. The HCCI mode is more efficient than the SI mode because the HCCI mode enables the ICE to operate with leaner air/fuel mixtures than when in the SI mode.
The HCCI mode generates a flameless release of energy with a lean air/fuel mixture by compressing the air/fuel mixture to a point of auto-ignition. The HCCI mode can provide improved fuel economy and generate lower emission levels than the SI mode. However, since there is no direct initiator of combustion, the ignition process may be inherently challenging to control.
For example, combustion during the HCCI mode may be controlled based on temperature. The temperature may be based on an engine coolant temperature (ECT) signal from an ECT sensor. During a cold start of the ICE, the HCCI mode may be disabled until the ECT signal is greater than or equal to a predetermined temperature. Enabling the HCCI mode during the cold start may cause an unstable and degraded auto ignition.
During the HCCI mode, if the air/fuel mixture is ignited by compression before the predetermined temperature is reached, noise, damage to engine components, misfires, and/or an engine stall may occur. This increases emissions and reduces drivability of the ICE. For the above reasons, the HCCI mode may be delayed until the ICE is heated to the predetermined temperature.